humming vs sibilant

humming

noun

  • The sound of something that hums; a hum. 

adj

  • Making a hum sound. 

sibilant

noun

  • A consonant having a hissing or hushing sound such as the s or sh in sack or shack. 

adj

  • Characterized by a hissing or hushing sound such as the s or sh in sack or shack. 

How often have the words humming and sibilant occurred in a corpus of books? (source: Google Ngram Viewer )